Controllable vibration devices include controllable linear dampers, mounts and the like whose damping may be controlled. In particular, field responsive fluid devices include any fluid whose apparent viscosity responds to an applied field (electrical or magnetic). One class of such field responsive fluids are MagnetoRheological (hereinafter MR) fluids, i.e., a mediums having magnetically-soft particles suspended in a carrier fluid. One such MR Fluid is described in commonly assigned U.S. Pat. No. 5,382,373 to Carlson et al. MR dampers are known and include linear acting varieties, i.e., those which include piston members which reciprocate in a damper body along a primary damper axis. In other words, linear-acting devices can be used for damping linear motion or for providing controllable dissipative forces.
For example, MR devices have been found useful in a wide variety of applications. MR dampers have been incorporated in vehicle engine mounts. One such device is taught in commonly assigned U.S. Pat. No. 5,398,917 to Carlson et al. Other MR fluid devices with electrical adjustment means are taught in the commonly assigned U.S. Pat. No. 5,277,281 entitled "Magnetorheological Fluid Dampers". U.S. Pat. No. 5,284,330 to Carlson et al. describes axially acting (linear) dampers and devices including sealless designs. Multi-Degree of freedom MR devices are described in U.S. Pat. No. 5,492,312 to Carlson entitled "Multi-Degree Of Freedom Magnetorheological Devices And System For Using Same.
A number of problems have emerged in developing viable controllable fluid dampers. First, the insertion of a valve within the piston of an MR damper as shown in FIGS. 9a-9d of U.S. Pat. No. 5,277,281, is generally complex and requires the electrical wire lead to be sealed. Further, having the controllable valve within the piston limits the space for the use of passive damping in conjunction with the controllable pathway. Therefore, a damper construction is needed which is cost effective and easy to manufacture. Also, in some instances, power may be unavailable, yet some damping adjustment may be desired. Therefore, a need exists for a device which is externally and mechanically adjustable by a user without the need for expensive electronic controls and electrical hardware. Additionally, the field responsive fluids tend to be costly, therefore there is a need for devices which utilize less fluid.
The foregoing illustrates limitations known to exist in present devices and methods. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.